* cipher/kdf.c (hash, argon2_genh0_first_blocks): New for Argon2.
(argon2_init, argon2_ctl, argon2_iterator): Likewise.
(argon2_compute_row, argon2_final, argon2_close): Likewise.
(argon2_open): Likewise.
(balloon_open): New for Balloon.
(_gcry_kdf_open, _gcry_kdf_ctl, _gcry_kdf_iterator): Add new API.
(_gcry_kdf_compute_row, _gcry_kdf_final, _gcry_kdf_close): Likewise.
* src/gcrypt-int.h: Add declarations for new API.
* src/gcrypt.h.in: Likewise.
(enum gcry_kdf_algos): Add GCRY_KDF_ARGON2 and GCRY_KDF_BALLOON.
(enum gcry_kdf_subalgo_argon2): Add GCRY_KDF_ARGON2D,
GCRY_KDF_ARGON2I, and GCRY_KDF_ARGON2ID.
* src/libgcrypt.def, src/libgcrypt.vers: Update.
* src/visibility.h: Likewise.
* src/visibility.c: Add new API.
* tests/Makefile.am (t_kdf_LDADD, t_kdf_CFLAGS): Enable use of pthread.
* tests/t-kdf.c (check_argon2): New, not enabled yet.